A number of synthetic and naturally occurring water soluble polymers have been developed which exhibit, in aqueous solution, superior thickening and flocculating properties. These have proven valuable in a number of commercial applications such as wastewater treatment and water purification, papermaking, petroleum recovery and oil drilling mud stabilizers.
Water treatment polymers such as the above are commercially important in some applications because of their effectiveness in flocculating suspended solids from aqueous systems. Common applications include use in clarification, thickening and filtration unit operations. More specific examples of these applications include clarification of drinking water or water used in coal washing applications, improvement in the retention of solids in papermaking machines, improving the filtration rate of and increasing the sludge cake solids in municipal and industrial waste treatment operations. The mode of action is generally a destabilization of the suspension of solids through coagulation and flocculation mechanisms. The polymer is adsorbed onto the suspended solids which results in a destablization of the suspensions, thereby clumping or aggregating them into a mass large enough to be separated from the solution.
Water treatment emulsion products are dispersions of aqueous solutions of polymers in oil. The finely divided, dispersed internal aqueous phase contains relatively high concentrations of water soluble polymer, often in excess of 50%, as well as a variety of additives such as buffers, chelants, salts and polymerization modifiers such as branching agents and chain transfer agents. These products generally contain one or more surfactants which add substantially to the usefulness of the product by improving stability and handling characteristics. The particle size of the dispersions is normally in the range of 0.1 to 10 .mu.m, but systems outside of these particle size ranges are certainly feasible.
A key step in the preparation of a product like the above in a water treatment application is the release of the polymer from the oil suspension into the medium being treated. The polymer must make intimate contact with the suspended solids for it to be effective. Since these organic flocculants are relatively expensive, there is a strong economic incentive to develop a product that provides for the greatest efficient use of its polymer content.
When the above product is added to water, a dispersion of oil droplets containing the finely divided particles of water soluble polymer is formed in water. The release of the polymer from this internal aqueous phase to the external aqueous phase is necessary for the polymer to modify the characteristics of the external aqueous phase. This release process is often called "inversion".
The inversion process is subject to much current investigation, and is still not completely understood. First, a dispersion of polymer-containing-oil is added to dilution water and mixed thoroughly. Generally, the next step that is observed is swelling of the internal polymer containing droplets, presumably due to the chemical potential differences between the internal and external aqueous phase (osmotic pressure). Finally, the oil phase will no longer be able to contain the swollen polymer droplets, and a release of polymer into the external aqueous phase will occur.
One technique that has been proven to be of great commercial utility has been the addition of a water soluble surfactant to products like the above after the polymerization has been completed. A variety of such surfactants can be used; one class that has been very successful commercially is the group of products known as alkyl phenol ethoxylates (APE), in particular nonyl phenol ethoxylates with degrees of ethoxylation ranging from 4-15 moles per mole of nonyl phenol.
The inversion step wherein the polymer is released from the internal aqueous phase is improved using a surfactant, sometimes called an activating agent whose activity is dependent upon the dilution water chemistry, temperature, the ionic strength of the polymer and the effects of whatever additives might be present.
U.S. Pat. Nos. 3,624,019 and 3,734,873 to Anderson et. al. teach the basic inversion polymerization technology whereby water soluble vinyl addition polymers are polymerized using a number of surfactants such as ethoxylated alkyl phenols, polyethoxylated vegetable oils and alkyl alcohols and the condensation products of the reaction between a higher fatty alcohol and ethylene oxide. The emulsion is added to excess water to extract the polymers by way of the inversion process.
U.S. Pat. No. 4,147,681 to Lim et. al. teaches a water-in-oil emulsion polymerization process wherein the acrylamide monomers are polymerized through self-inversion using sulfated castor oil. Polyoxyethylene vegetable oil and polyoxyethylene fatty alcohols are disclosed as one of a number of surfactants that bring about the inversion but there is no teaching of the use of a surfactant after polymerization. U.S. Pat. No. 3,997,492 to Kane teaches a stable water-in-oil emulsion of water soluble polymers whereby the surfactant for inversion is selected on the basis of the properties of the organic continuous solvent phase. No specific surfactants are disclosed as particularly useful but are determined on the basis of a mathematical formula, the cohesion energy ratio of the emulsion and the hydrophilic/lipophilic balance (HLB). This adapts the choice of the surfactant to the particular chemical environment or application.
U.S. Pat. No. 4,252,706 to Phillips et. al. teaches a method for precisely controlling the dissolution rate of high molecular weight water soluble vinyl polymers. Again, all the suitable surfactants are not specifically listed but suggested are the non-ionic water soluble surfactants such as nonyl phenol ethoxylates, sorbitan monooleate and the like which are those commonly used in the inversion polymerization process. Finally, U.S. Pat. No. 4,024,097 to Slovinsky et. al. teaches the precipitation of self-inverting polymers in water-in-oil emulsions wherein the surfactant is a fatty amide or alkanolomides such as sodium oleate or Span. There is no disclosure or suggestion of the inversion process of the present invention nor is there the use of castor oil as the activation surfactant.
It is clear then that the process of making water soluble vinyl addition polymers by self-inversion of a water-in-oil polymer containing emulsion is well known in the art and many known surfactants have been found useful as polymerizers in the first step. However, for the most part, only ethoxylated alkyl phenols have been used as activating or release agents since they are inexpensive and generally provide an efficient dissolution of acrylamide polymers in water. However, there has been increasing concern regarding the environmental impact of these compounds, particularly the by-products that result from the biodegradation of these surfactants.
It is an object of the present invention to provide a water soluble vinyl addition polymer with superior thickening and flocculating characteristics that may be released from a standard water-in-oil emulsion using a safe, environmentally friendly activating surfactant. It is a further object of the present invention to provide a method for the self-inversion of a water soluble vinyl addition polymer using a release agent that is both environmentally friendly and provides superior thickening and flocculation properties. It is a further object of the present invention to provide an environmentally safe release agent comprised of an alkoxylated castor oil that enhances the release of the polymer when the water-in-oil emulsion is added to the excess water.